Until the late 1960's ophthalmological surgical techniques for cataract removal were performed by using standard intracapular cataract extraction techniques which, although generally satisfactory, require a prolonged recovery time as long as several months. Since that time, a procedure known as phacoemulsification, or use of an ultrasonic probe to break up and remove cataracts, has become widely used because it offers a remarkable decrease in recovery time. Indeed, a patient can sometimes return to work the day after surgery with this technique.
The procedure for removal of cataract tissue is described in an article entitled "History of Emulsification and Aspiration of Senile Cataracts," by Charles D. Kelman and appearing in Transaction of American Academy of Opthalmology and Otoaryngology, volume 78, January-February, 1974, pages OP5-13 (originally presented at the 78th Annual Meeting of the American Academy of Ophthalmology and Otoaryngology, Dallas, Texas, Sept. 16-20, 1973).
Generally speaking, a tip in the form of a hollow tube is inserted into the anterior chamber of the eye, through a small incision, into contact with the cataract tissue. The tip is vibrated by a hand-held probe at an ultrasonic rate, and hydrodynamic flow of a saline solution is established in order to prevent collapse of the anterior chamber. As particles of the cataract tissue are cut from the cataract mask, the particles are suspended in the saline solution and removed from the chamber through the tip of the ultrasonic probe by vacuum aspiration. In the case of hard cataracts, those particles with a tendency to slide into contact with the walls of the chamber have an abrasive character. Since certain portions of the eye including the chamber walls are prone to abrasion sensitivity, the cataract particles must be quickly, and as possible, removed from the chamber. This is done by aspiration through the hollow tip of the ultrasonic probe.
During aspiration of cataract tissue, the tip of the ultrasonic probe must be very carefully manipulated under the field of a microscope in order to prevent aspirating other than cataract tissue and to ensure that all the cataract particles are removed from the chamber. Close control of the tip is especially critical at the peripheral regions of the cataract.
The tip must be able to effectively remove the cataract tissue without clogging or otherwise hindering the surgical procedure. Several improved ultrasonic probes have been developed for performing this and other delicate types of surgery as well as cleaning teeth and the like. These probes generally consist of a tip for cutting/cleaning material at the operation site, a handpiece for mounting the tip and associated circuitry, and a piezoelectric crystal or other means for supplying ultrasonic energy to vibrate the tip. My prior design disclosed in U.S. Pat. 4,169,984, is one such improved ultrasonic probe.
Despite the improvements that have been made, the prior ultrasonic probes have not proved to be as effective and efficient in removing the undesired tissue as they could be. As indicated above, the probe must first and foremost efficiently remove the undesired tissue from the surgical field. The vacuum lines of the prior art devices are often tortuous, adversely affecting the efficiency with which particles are aspirated. If clogging occurs, the surgery must be halted to clear the clogging or to change equipment. The delay in surgery increases the trauma and risk to the patient.
Piezoelectric crystal transducers have been commonly used to provide the ultrasonic vibrations of the probe tip. These piezoelectric crystals have been compression loaded as a protective measure since they have a tendency to break from shock loading and dynamic fatigue. In the past, the compression loading has obtained by positioning the crystal transducers between two elements which have been bolted together, applying compression to the crystal transducers. With this design, it is difficult to apply compression loading uniformly across the transducer surface, and breakage can occur either during mounting or in operation due to localized stresses. Also, the clamping bolts may be affected by thermal expansion and contraction from heating and cooling during probe operation. This changes the compression loading on the crystals, thus causing a shift in resonant frequency. Such a shift in resonant frequency directly affects probe cutting action. Avoiding any such fluctuations in cutting action is particularly critical to patient safety where, for example, the surgeon is cutting the peripheral regions of the cataract means.
Further, the previous ultrasonic probes that incorporating irrigation mechanisms with the aspiration elements have tended to be large and cumbersome and inefficient in the performance of th delicate surgery. The irrigation stream has tended to be misdirected, failing to provide most effective results. Irrigation streams provided by prior art devices have typically interfered with the surgeon's view of the ultrasonic tip/tissue interface.
A new and improved ultrasonic probe having (1) a substantially straight-through aspiration path, (2) irrigation and aspiration mechanisms contained in a small maneuverable housing, and (3) piezoelectric transducers continuously and uniformly loaded in compression is, therefore, needed.